This invention relates to a method and apparatus for determining the position of an object in a confined space.
The invention finds particular but not exclusive application in determining the contents of a bunker or silo by measuring the position of the top of the contents. It will be appreciated that the contents may be in the form of particulate solids or a liquid form. The invention is, however, not limited to this application and may be used for other purposes such as, for example, determining the position of a train in a tunnel or locating the position of an intruder in a room where a security situation is being monitored.
The invention operates on the well known radar principle of projecting a beam of high frequency radiation at an object, collecting the reflected signal and analysing the time delay to give a determination of the position of the object. One example of the application of this method to measure the contents of a bunker is disclosed in British Patent Application No. 2,020,507A.
The general application of the radar principle gives rise to many problems in practice, particularly those associated with variations in aperture and frequency components where the surface of the object being monitored is continually moving. For example, in a bunker which has been fed with particulate or liquid material there may be a spread of material across the surface which gives a constantly varying uneven surface. The radar may also be confused by material falling across the path of the beam. Errors may also be introduced due to a constant reflection from a projection such as a support within the bunker or standing waves can become a problem in any microwave system connecting the radar aerial to the microwave source.